The specter of antitrust action against four of the largest tech companies in the world has evolved into a parlor game among some in Silicon Valley: What antitrust suspect is the most vulnerable to a government-imposed action if it comes to that?

According to a range of experts contacted by MarketWatch, Facebook Inc. /zigman2/quotes/205064656/compositeFB+1.98%
and Apple Inc. /zigman2/quotes/202934861/compositeAAPL+2.85%
are most at risk if government regulators are serious about pursuing antitrust actions against Big Tech, though each of the four—Alphabet Inc. /zigman2/quotes/205453964/compositeGOOG+1.86%/zigman2/quotes/202490156/compositeGOOGL+1.82%
and Amazon.com Inc. /zigman2/quotes/210331248/compositeAMZN+0.91%
are the other two giants reportedly under scrutiny—face exposure in different ways from various agencies and countries.

“We’re finally getting to a place where we’re going to interrogate these unprecedented concentrations of information, and the power that accrues to them,” Shoshana Zuboff, a Harvard Business School professor and author of “The Age of Surveillance Capitalism: The Fight for a Human Future at the New Frontier of Power,” told MarketWatch.

She said Makan Delrahim, the Justice Department’s assistant attorney general, tipped his focus in a speech
last week in Tel Aviv, assessing one or two “significant players” in internet search, social networks, mobile and desktop operating systems, and electronic book sales.

Each of the four companies could be penalized to some degree—from injunctive (Apple) to structural (Facebook)—but a breakup of any kind is “highly unlikely,” says Herbert Hovenkamp, a professor at the University of Pennsylvania who teaches at both its law and business schools.

Those who closely follow U.S. regulators don’t expect radical changes but prescriptive measures that mollify lawmakers and privacy advocates. The big investment banks seem to be operating under the same presumption. For now, none of the four companies under regulatory scrutiny have received downgrades from top-level Wall Street firms.

For more: Analysts say not to worry about Big Tech’s antitrust investigations

One reason may be that while European regulators have a mandate to protect small companies, their U.S. counterparts focus on “consumer welfare” so it might be hard to argue lower prices (in the case of Amazon) or better products (Google, Apple and Facebook) are hurting consumers, Jefferies analyst Brent Thill concluded in a June 12 note
.

However, at the very least, they all could endure yearslong depressed market values, as International Business Machines Corp. /zigman2/quotes/203856914/compositeIBM+2.46%
and Microsoft Corp. /zigman2/quotes/207732364/compositeMSFT+2.34%
did before them when they were targets of federal antitrust probes, as Goldman Sachs pointed out in an analysis last week.

“We believe that not all FAANGs will survive this battle,” Needham analyst Laura Martin wrote in a June 17 note, noting a widely used acronym for large tech companies. “The fact that the FTC now has jurisdiction over Facebook and Amazon weakens their position as an investment alternative vs. Apple and Google (DOJ jurisdiction).”

MarketWatch asked Hovenkamp, Zuboff, and other experts to assess the regulatory threats for all four companies. They are listed here in order of consensus risk that some type of action will be taken.

Facebook

The 15-year-old company has achieved its status as the de facto social-media option for more than 2 billion members, allowing it to devour 83% of U.S. social ad spending this year, according to eMarketer, in part through acquisitions.

Tim Wu, a professor of law, science, and technology at Columbia University professor, estimates Facebook snapped up at least 92 companies—many of them competitors that included WhatsApp and Instagram—since 2007 without the federal government challenging one purchase. It shut down 39 companies, some of which may have represented future competitors, Wu says.

Some analysts claim Instagram, which Facebook acquired for $1 billion in 2012, is now worth about $100 billion, largely because it is the most popular social network among teens, according to a Piper Jaffray survey.

“The rest have plenty of enemies banging pots, especially Amazon, but in terms of the actual law, Facebook is the low-hanging fruit,” says Wu, author of “The Curse of Bigness: Antitrust in the New Gilded Age.”

Vanderbilt University law professor Rebecca Allensworth puts it more bluntly: She considers Facebook the most vulnerable of the four because of “its dominant status in an easily defined market.” The solution is obvious, she says: Cleave off social-media properties WhatsApp and Instagram, which were acquired for a combined $20 billion since 2012.

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